1. Field of the Invention
The present invention relates to a sintered body for manufacturing a ceramic substrate. The present invention also relates to a ceramic substrate, and a manufacturing method thereof.
2. Description of Related Art
In accordance with recent developments in highly integrated electronic devices, there is a demand for fine and very dense wiring on a substrate. In order to meet the demand, a method in which the fine wiring is provided on a ceramic substrate using a thin film is widely employed. When a via conductor is formed penetrating the ceramic substrate, both sides of the substrate can be effectively used, so that very dense wiring can be realized. For this reason, this method is widely used, and this substrate is put into practical use for assembling semiconductor packages.
When the wiring becomes finer, blow holes in the ceramic, opening onto the substrate surface, might be a cause of disconnection or high resistance. When the via position is slightly displaced, it could be a cause of defective electric continuity. Therefore, in order to form fine and very dense wiring using a thin film, it is necessary that the ceramic substrate be dense, that the number of blow holes be small, and, further, that the surface be flat. In addition, the positional accuracy of the via must be high. Further, there is a strong requirement for a reduction in the cost.
Conventionally, the following method is employed to manufacture a ceramic substrate having the via described above. First, a ceramic green sheet is provided. After the ceramic green sheet has been subjected to punching so as to form a predetermined shape, through-holes are formed at predetermined positions. Next, the through-holes are filled with metallic paste. At least two layers of green sheets that have been processed in this way are laminated. The thus obtained laminated body is subjected to binder-removal treatment and then fired or burned. In this way, the substrate is formed. In this case, a substrate that has warped badly is corrected or rejected. The substrate is then cut into a predetermined shape and polished, and the manufacture of the substrate is completed.
In the above manufacturing process, when the thickness of the substrate is small, it is possible to fill the through-holes with metallic paste after the green sheets have been made into a laminated body. However, in many cases, it is necessary to fill the through-holes with metallic paste for each green sheet. The number of substrates obtained from one sheet of green sheet lamination body is approximately 1 to 4. When the size of the green sheet lamination body is increased so as to increase the number of substrates obtained from one sheet of green sheet lamination body, not only the working efficiency is lowered but also the positional accuracy of the via is deteriorated. After all, the unit number handled in the process is approximately the same from the first to the final stage. Accordingly, the number of the obtained substrates, per one process or one device, is small. Therefore, a sufficiently high mass-production effect cannot be provided, and it is impossible to reduce the cost. Further, due to the defective electric continuity caused by a displacement of the via in the process of lamination and also due to the warping of the substrate, it is difficult to reduce the cost.